Presently, a variety of coating materials are used for painting exterior parts of materials such as construction materials, daily commodities, etc., including automotive parts. In such uses, it is necessary that the coating material compositions exhibit the following properties: a) impact resistance for an outer environment, b) heat resistance for high temperature painting processes, c) improved surface polishing property for better appearance, and d) improved dispensability to maintain uniform rigidity.
Among these coating materials, the polyamide resins polyamide-6 and polyamide-66 are being widely employed as coating material compositions since they possess not only good mechanical properties such as strength, rigidity, toughness, abrasion resistance, etc., but also favorable heat resistance, grease and oil-proof, chemical tolerance and molding properties.
Disadvantages of these materials, however, are shown in the following:
1) British Patent Nos. 387903 and 327978 and German Patent No. 3827668; even though the crystallized polyamide and polyolefin resin composition, supplementing an inorganic filling agent, proves to have good heat resistance, rigidity and stabilized measurement, their light mass design may not be fully materialized due to their insufficient surface polishing and molding properties and high specific gravity.
2) U.S. Pat. No. 4,923,924, British Patent No. 2951035 and German Patent No. 3834912; even though the modified polyphenylene oxide or modified polyphenylene ether resin composition has relatively good properties in terms of impact resistance and heat resistance, their inferior properties such as fluidity, photo-resistance and chemical tolerance make them less suitable for exterior materials and so of limited utility.
3) With respect to amorphous polyamides, the amorphous polyamide (U.S. Pat. No. 2,696,482) consisting of a polycondensate of bis(4-aminocyctohexyl)methane and isophthalic acid and the amorphous polyamide (U.S. Pat. No. 3,597,400) of a polycondensate consisting of bis(4-aminocyclohexyl)methane, hexamethylene diamine, isophthalic acid and terephthalic acid both exhibit poor fluidity due to their high melting points; injected molding is therefore very difficult. Also, since the amorphous polyamide and thermoplastic elastomer alloys have poor fluidity, molding is not easy. Accordingly, the present inventors have sought to overcome these defects of the prior art and so have proposed: after adding polyamide copolymer to polyamide, the mixture is blended with a thermoplastic elastomer having good impact modification at low temperature together with a fluoride polymer for better surface polishing and painting, a thermoplastic resin composition having good painting and surface polishing properties is obtained.